Massive storm on Neptune is mysteriously shrinking, but why?

16 Feb 2018

Image of Neptune taken by Voyager 2 at a distance of 4,950km from the planet’s north pole. Image: NASA

A massive storm located on the surface of Neptune is mysteriously shrinking, but there might be an answer as to why.

While Jupiter is famous for its enormous, centuries-old storm known as the Great Red Spot, Neptune also has its own massive storm, but without the cool-sounding name.

Since the late 1980s, a number of storms have been discovered on Neptune’s surface after the flyby of Voyager 2, but it is only since then that the Hubble Space Telescope has had the sharpness in blue light to track these elusive features.

This includes two dark storms that appeared in the 1990s but suddenly vanished, and now the massive storm identified in 2015 is shrinking.

The storm shares similar characteristics with Jupiter’s storm as it swirls in an anticyclonic direction, pulling up huge amounts of material from deep inside the ice giant’s atmosphere. It has been important to astronomers because it gives us a glimpse of the planet’s deep winds.

However, while Jupiter’s storm has raged for at least the past 200 years, this Neptune storm and its dark vortices are just a few years old, and are now the first to be photographed in the midst of dying.

Adding to the mystery, predictions made by astronomers on how the storm would behave have proven to be wrong.

“It looks like we’re capturing the demise of this dark vortex, and it’s different from what well-known studies led us to expect,” said Michael H Wong of the University of California, Berkeley.

“Their dynamical simulations said that anticyclones under Neptune’s wind shear would probably drift toward the equator. We thought that once the vortex got too close to the equator, it would break up and perhaps create a spectacular outburst of cloud activity.”

Rather, it has simply faded away, possibly because it is drifting toward the south pole, instead of northward towards the equator.

Unlike Jupiter’s alternating wind jets, which appear as its famous bands surrounding the planet, Neptune’s are far less constrictive and numerous, meaning there is more room to wander.

Colm Gorey was a senior journalist with Silicon Republic